1. Field of the Invention
This invention relates to fastener assemblies and is directed more particularly to a fastener assembly for retaining sheets of roofing material on a roof.
2. Description of the Prior Art
Stress plates for securing a sheet of roofing material, often referred to as a "membrane", to a roof deck, or other structural member or roof surface, are generally known. Such plates usually are secured to the roof deck, structural member or surface by fasteners which pass through openings in the plates, through the membrane, and engage the deck or structural member. Plates of this type are shown, for example, in U.S. Pat. No. 4,787,188, issued Nov. 29, 1988 to Colin R. Murphy and U.S. Pat. No. 4,945,699, issued Aug. 7, 1990 to Colin R. Murphy.
The stress plates commonly are used to clamp membranes to the roof deck. In practice, the membrane is applied to the roof deck at a seam portion defined by an overlapping disposition of membranes. A lower membrane is fastened to the roof deck by use of the stress plates and fasteners, typically screws. An upper membrane is lapped over the lower membrane in such a manner as to overlie the stress plates, with the upper membrane being secured to the lower membrane by a welded seam.
The stress plate is mounted on the lower membrane with an undersurface of the stress plate in clamping engagement with the lower membrane. It has generally been thought that loosening of a stress plate, as by loosening of a retaining screw, permits the membrane to slide out from under the stress plate. It has been believed that tight compression of the membrane by the plate is the way to retain the membrane in place in the event of high winds, and the like.
It has been found, however, that high winds simply rip the membrane from around the plate. Thus, while the plate may remain solidly attached to the roof deck, the membrane is nevertheless loosened or lost.
Accordingly, there is a need for stress plate assemblies capable of holding a membrane in place in high winds and resisting membranes tearing away from the plates.